1. Technical Field
This invention relates to a battery charge control apparatus for a vehicle, where the vehicle is provided with a prime mover driven by using fuel stored in the vehicle, power generation means for converting energy generated by the prime mover using the fuel into electrical energy, and a secondary battery that stores the electrical energy.
2. Related Art
A known battery charge control apparatus, as disclosed in Japanese Patent Application Publication No. 2006-166639, is adapted to set a power for charging a secondary battery as a function of a maximum power that allows a cost of fuel consumption per unit electrical power to be kept equal to or smaller than a target cost. In general, when a power requirement of a drive wheel is small, an operating point of an engine is shifted to a higher load by increasing a power output of a generator of the vehicle, which leads to enhancement of fuel usage efficiency of the engine. The apparatus as disclosed above is thus operative to increase the power output of the generator to charge the secondary battery when the power requirement of the drive wheel is small.
Meanwhile, when an amount of battery charging power is increased, a battery charging current becomes larger, which will probably lead to an increase in charging loss due to the presence of internal resistance of the battery. According to findings of a study of the inventors of the present application, since the internal resistance of the secondary battery becomes larger as the temperature of the secondary battery decreases in a winter season or the like, the charging loss becomes larger, which leads to a danger that a decrease in fuel utilization efficiency may exceed a benefit of reducing of the fuel consumption in low cost power generation.
In consideration of the foregoing, exemplary embodiments of the present invention are directed to providing a battery charge control apparatus for a vehicle, where the vehicle is provided with a prime mover driven by using fuel stored in the vehicle, power generation means for converting energy generated by the prime mover using the fuel into electrical energy, and a secondary battery that stores the electrical energy.